Hi there!
Okay, so your problem is that when you are muting the tab you are really muting the website and since you are duplicating the tab 3 times you must have the same website on each tab, therefore you are muting the website, not the individual tab.
There is not a way to fix this on Google Chrome because you would have to unmute the whole website in order to hear sound on your tab, unfortunately, there is no way to mute the individual tab on its own.
-Your friend in tech, ASIAX